1. Field of the Invention
The present invention relates to an automatic sheet conveying mechanism, and more particularly to an automatic sheet conveying mechanism optimally used as an automatic document conveying mechanism for conveying a plurality of documents in a device such as facsimile machine, image scanner, or the like.
2. Description of the Related Art
The present invention relates to an automatic sheet conveying mechanism of a facsimile machine or image scanner, wherein the automatic sheet conveying mechanism automatically conveys a plurality of single sheets for reading images, processing, and stamping (for example, see the Japanese Unexamined Patent Publication No. 2-215666).
An automatic sheet conveying mechanism 1000 in an earlier embodiment in the process of developing the invention is shown in FIG. 1. It comprises a pair of upper casing 1001a and lower casing 1001b divided in upper and lower parts. Each casings 1001a and 100lb are provided with sheet guide plates 1001d and 1002 which are made of separate materials from the corresponding casings 1001a and 100lb. Sheet guide plates 1001d and 1002 partition therebetween a sheet conveying path 1003 to convey sheets between the sheet guides 1001d and 1002, a sheet insertion port 1004 opened upstream of the sheet conveying path, and a sheet discharge port 1005 downstream of the sheet conveying path.
The sheet conveying path 1003 is composed of a lead-in part 1003a for leading the sheet inserted from the sheet insertion port 1004, a bent part 1003b bent downward from the lead-in part 1003a, and a processing part 1003c extending toward the discharge port 1005 which is integral with the bent part 1003b. Lead-in part 1003a has a sufficient width for inserting a plurality of sheets.
In the sheet conveying path 1003, sheet forward feed means 1006 disposed at the lead-in part 1003a, separating conveying means 1007 disposed in the bent part 1003b, sheet conveying means 1008 disposed in the processing part 1003c, a contact type image sensor 1009, and sheet discharge means 1010 are sequentially disposed.
The sheet forward feed means 1006 is for feeding forward the sheet disposed in the lead-in part 1003a to the downstream side, and is furnished with a forward feed roller 1006a confronting the lead-in part 1003a of the sheet conveying path 1003 from the lower casing 100lb. Above the forward feed roller 1006a, a pressing member 1006b is confronting the lead-in part 1003a of the sheet conveying path 1003 from the upper casing 1001a, being supported by the upper casing 1001a in a state free to move forward and backward in the confronting direction. The pressing member 1006b has a flat pressure bearing surface b1. On this flat pressure bearing surface b1, one extension spring member 1006c is stretched in a direction approximately orthogonal to the sheet conveying direction, with the both ends fixed on the upper casing 1001a. The pressing member 1006b is thrust to the forward feed roller 1006a side by this one extension spring member 1006c, and by this thrusting force, the sheet fed into the lead-in part 1003a is held together with the forward feed roller 1006a. In this state, by further rotating the forward feed roller 1006a, the sheet fed into the lead-in part 1003a is sent to the bent part 1003b at the downstream side.
The separating conveying means 1007 disposed in the bent part 1003b is provided with sheet conveying roller 1007a. The sheet conveying roller 1007a is confronting the bent part 1003b of the sheet conveying path 1003 from the sheet conveying roller 1007a. Above the sheet conveying roller 1007a is confronting a separating member 1007b projecting to the bent part 1003b of the sheet conveying path 1003 from the upper casing 1001a. The separating member 1007b is thrust to the sheet conveying roller 1007a side by a spring member 1007c. Furthermore, the separating member 1007b, in order to separate the sheets one by one, is provided with a separating part 1007d projecting into the sheet conveying roller 1007a for pressing the sheet together with the sheet conveying roller 1007a, and a pad 1007e confronting the sheet conveying roller 1007a as being disposed opposite to the separating part 1007d, and by this separating part 1007d, the end of the sheet fed into the lead-in part 1003a is separated obliquely so that the upper end side may be inclined to the upstream side, while only the lowermost sheet is held between the pad 1007e and sheet conveying roller 1007a by the thrusting force of the spring member 1007c. In this state, by rotating the sheet conveying roller 1007a, only the lowermost one of the sheets from the lead-in part 1003a is sent into the processing part 1003c at the downstream side from the bent part 1003b. In this constitution, the separating direction by the separating member 1007b of the separating conveying means 1007 is intersecting with the conveying direction of the sheet conveying means 1008, and therefore multiple feed is prevented, and only the lowermost sheet can be conveyed easily.
The sheet conveying means 1008 disposed in the processing part 1003c is to convey the sheets individually separated by the separating conveying means 1007 to the image contact type image sensor 1009 side, and it is provided with a driven roller 1008a disposed on the upper casing 1001a and a driving roller 1008b disposed on the lower casing 100lb. The driving roller 1008b is set so as to rotate at a higher peripheral speed than the sheet conveying roller 1007a, so that joint conveyance of sheets is prevented.
The contact type image sensor 1009 is to separate and scan the image which is the two-dimensional information of the conveyed sheet in every pixel, and comprises a contact type image sensor main body 1009a. The contact type image sensor main body 1009a is fixed to the lower casing 100lb of bolts 1009c through a frame 1009b, and comprises a contact glass 1009d confronting the processing part 1003c. In the conventional apparatus, the contact glass 1009d slightly projects upward from the upper surface of the sheet guide 1002, and in order that the sheet may not be caught on the contact glass 1009d when conveying and moving the sheet, it is furnished with a cut surface 1009e of which upstream side end face is cut obliquely.
The sheet discharge means 1010 is for discharging the sheet being read and processed by the contact type image sensor 1009a into the sheet discharge port 1005, and is composed of a driven roller 1010a mounted on the upper casing 1001a and a driving roller 1010b mounted on the lower casing 100lb.
Thus, in the constitution shown in FIG. 1, the sheet guide plates 1001d, 1002 for partitioning the sheet conveying path 1003 were formed of separate members for the corresponding casings 1001a, 100lb, it was difficult to achieve the positioning precision of the sheet conveying path 1003 with respect to the functional parts for composing the sheet forward feed means 1009, separating and conveying means 1007, sheet conveying means 1008, contact type image sensor 1009, and sheet discharge means 1010, and it was hence difficult to maintain a high performance.
For example, in the case of the lower casing 1001b, due to the effects of assembling precision of the sheet guide plate 1002 and lower casing 100lb, if the sheet guide plate 1001 is sinking too much as compared with the lower casing 1001b, the functional part mounted on the lower casing 100lb is projecting too much into the sheet conveying path 1003, which often resulted in duplicate feed or noise due to deflection of the sheet. On the other hand, if the relative position of the sheet guide plate 1002 to the lower casing 100lb is too high, the functional part mounted on the lower casing 100lb cannot be projected sufficiently into the sheet conveying path 1003, and the sheet conveying capacity is lowered, and the conveying delay may be caused.
Besides, in the constitution in FIG. 1, since the pressing member 1006b is thrust to the forward feed roller 1006a side in the state of laying the extension spring member 1006c over the flat pressure bearing surface b1, although the extension spring member 1006c can be uniformly abutted against the pressing member 1006b, it is difficult to apply the thrusting force of the extension spring member 1006c uniformly over the whole stroke of the pressing member 1006b, or to set the initial load.
More specifically, when the pressure bearing surface b1 is formed flatly, since the edge of the pressure bearing surface b1 slides on the extension spring 1006c, a fluctuation occurs in the thrusting force between the both ends and the middle part of the pressure bearing member b1, and the thrusting state of the extension spring member 1006c to the pressure bearing surface b1 is not stabilized. Accordingly, the initial load hardly settles at the predetermined set value.
Moreover, since the number of sheets fed into the lead-in part 1003a of the sheet conveying path 1003 is always different generally, the stroke in the pressing direction of the pressing member 1006b is set relatively large. Accordingly, by the behavior of the pressing member 1006b in the pressing direction, the fluctuation of thrusting force is emphasized. When such fluctuation of thrusting force occurs, if the thrusting force is excessive, the force for pressing the sheet is too strong, duplicate feed of sheets occurs, or if too weak, the sufficient forward feed force in the case of many sheets cannot be obtained, and delay in conveying occurs.
In the constitution in FIG. 1, by thrusting the pressing member 1006b merely by a single extension spring member 1006c, the sheet fed into the lead-in part 1003a was held between the pressing member 1006b and forward feed roller 1006a, it was extremely difficult to set the thrusting force of the extension spring member 1006c.
Explaining more specifically, the number of sheets fed into the lead-in part 1003a of the sheet conveying path 1003 is always different, and when the number of sheets is large, it is necessary to hold the sheets firmly to obtain a sufficient forward feed driving force, or when the number of sheets is small, it is necessary to hold weakly to prevent duplicate feed.
Therefore, if the thrusting force of the extension spring member 1006c is too strong, when the number of sheets is small, duplicate feed of sheets may occur, and if too weak, when the number of sheets is many, sufficient forward feed force cannot be obtained, and delay in conveying occurs.
Also in the constitution in FIG. 1, in order to convey only the lowermost sheet by preventing duplicate feed, the separating direction by the separating member 1007b of the separating conveying means 1007 is intersecting with the conveying direction by the sheet conveying means 1008, and therefore when the sheet reaches the faster sheet conveying means 1008 than the conveying speed of the sheet conveying roller 1007a and a tension is generated between the sheet conveying roller 1007a and the sheet conveying means 1008, the separating member 1007b may be kicked up by the sheet on which this tension is acting. As a result, duplicate feed of sheets occurs the moment the separating member 1007 is kicked up.
Also in the constitution in FIG. 1, in order to convey only the lowermost sheet by preventing duplicate feed, the separating part 1007d of the separating member 1007b is projecting to the sheet conveying roller 1007a, and the sheet is held against the sheet conveying roller 1007a, and therefore it was extremely difficult to specify the shape of the separating part 1007d of the separating conveying means 1007.
More specifically, when the separating part 1007d is projecting too much to the sheet conveying roller 1007a side, the sheet cannot get in between the two, and conveying failure may occur, or if the projection is too small, a plurality of sheets may be held, and duplicate feed may occur.
Also in the constitution in FIG. 1, since the contact type image sensor main body 1009a is fixed to the lower casing 100lb by the bolt 1009c, frame 1009b, etc., in the case of maintenance or replacement work of the contact type image sensor main body 1009a, it was required to detach the sheet guide plate 1002 from the lower casing 100lb, loosen the bolt 1009c, and dismount the contact type image sensor main body 1009a from the frame 1009b. It hence took much labor in maintenance work, which could not be done by the user alone.
Also in the constitution in FIG. 1, since the cut surface 1009e having the upstream side end face cut obliquely is formed on the contact glass 1009d of the contact type image sensor main body 1009a, the manufacturing cost of the contact glass 1009d was higher. In particular, since the contact type image sensor main body 1009a is relatively high in frequency of replacement, it pushed up the maintenance cost.
Instead of the cut surface 1009e of the contact glass 1009d, a film-like Lumilar may be adhered to the contact glass 1009d, but in this case, the contact type image sensor 1009 must be replaced together with Lumilar, which means also a high maintenance cost.
The invention is devised in the light of the above problems, and it is hence a primary object thereof to present an automatic sheet conveying mechanism capable of setting the projection extent of functional parts into the sheet conveying path precisely, and preventing occurrence of unusual sound or delay in sheet conveyance.
It is also an object of the invention to present an automatic sheet conveying mechanism possessing a precise sheet forward feed function by stabilizing the sheet pressing force when feeding the sheet forward.
It is also an object of the invention to present an automatic sheet conveying mechanism possessing an appropriate sheet forward feed function regardless of the number of sheets.
It is also an object of the invention to present an automatic sheet conveying mechanism capable of preventing duplicate feed of sheets by preventing kick-up of the separating member.
It is also an object of the invention to present an automatic sheet conveying mechanism capable of securely preventing defective conveyance or duplicated feed of sheets in the separating conveying means.
It is also an object of the invention to present an automatic sheet conveying mechanism easy in the maintenance work of contact type image sensor when composing an automatic document conveying mechanism.
It is also an object of the invention to present an automatic sheet conveying mechanism low in the maintenance cost of contact type image sensor when composing an automatic document conveying mechanism.